J.R. Smith, who is 6-foot-6 and muscle-armed, who can dunk a basketball out of a standing jump and, when necessary, can outrun nearly everyone on the court, is an oddly unimposing man.

He is slender and narrow-eyed. He carries himself with sloping shoulders, unhurried. If his deadpan look is a pretense, a tactic meant to entrap the opponent, then the Knicks — filled with hope and bravado as they start their playoff season today — have discovered its virtues, finally.

This is no small revelation for a team that has struggled since the generation of Patrick Ewing and the erratic John Starks to find a consistent option to its star player.

At Madison Square Garden this afternoon, the Knicks and Celtics revive a rivalry. The Celtics will lead with Kevin Garnett and Paul Pierce, and the Knicks, of course, with Carmelo Anthony, the NBA’s leading scorer.

Smith will be waiting on the bench when the game starts, and once installed in the lineup he will be the one lurking on the wing. Once considered by conventional wisdom to be too selfish or too cocksure, or even disobedient, he has become Anthony’s surefire sideman.

Smith, 27, was the team’s second-leading scorer with 18.1 points a game. Alongside brittle, older teammates, no Knick played more minutes than Smith this season. And in the past five weeks, when he averaged more than 24 points, he has done something rare for a professional athlete — transforming his game in the middle of the season.

"Yes, it feels good," he said yesterday after the Knicks’ last practice before the postseason. His voice was muted. "Yes, because I’ve waited so long to hear good comments about me."

DAD’S SPIN ON THINGS

Getting to this point has been an odyssey for Smith. He played his junior and senior years of high school for St. Benedict’s Prep in Newark after transferring from Lakewood High School. Described this week by the Rev. Edwin Leahy, St. Benedict’s headmaster, as a "man-child," Smith eschewed college and was a first-round draft pick of the New Orleans Hornets in 2004. He was cast off two years later to the Denver Nuggets, where coach George Karl bristled publicly about Smith’s disregard for game plans and play calling.

His time with the Knicks has not included clashes with the former coach, Mike D’Antoni, or the present coach, Mike Woodson. But uneven play and criticism of his choices on the court persisted — at least until early last month.

What then has changed?

A player who only recently would unflinchingly shoot from all angles and distances on the court, has discovered other resources in his game. Smith now routinely puts his head down and drives to the basket and winds up on the free-throw line almost as often as he takes his trademark long-range jumper.

In basketball-speak, this is playing "inside-out." It gives defenders the jitters because their fear of Smith’s outside shooting is nearly matched now by their apprehension that he will run around them.

"The game is easier now," Smith said, almost with relief. "I shoot when I’m open. I pass or drive when I’m not. And I end up shooting fouls."

Credit, he said, belongs with Woodson, and with his father.

"Keep your arm at a right angle at the elbow," Smith said, as if in recitation. "Then shoot. Make sure the ball spins off your fingers. Give it the spin, so when you hit the shot, the ball will spin back to you.

"That’s all from my dad."

WATCHING & WAITING

Earl Smith sat in the living room of his home in Lakewood on a recent evening watching the Knicks on a 50-inch TV, offering a free-flowing commentary to a visitor. It angered him when the broadcasters labeled every missed shot by his son as a "poor decision."

"That’s what they do," he said. "That’s what they always do."

Earl Smith was drawing on his own experience as a junior college player who routinely bewildered and frustrated coaches. A mason by trade, he would use his free time to play in the summer leagues of Monmouth County. He would shoot hundreds of jumpers under a street lamp into chain-link nets.

"Ching, ching, ching," he said. "That was the sound I liked most."

Most of his analysis centered on why his son was not getting the ball, or not getting it in good position, or why he was plain overlooked.

"See what happens. They wait until the clock is running down until they give him the ball. So of course that affects his shot selection.

"They should just let J.R. bring the ball up. He looks for his teammates more than the other.

"Look at that," he said. "They all do whatever is good for Carmelo."

If Earl Smith was channeling any frustration from J.R., it was unclear. Earl is a bigger man than his son, broader, but their resemblance is unmistakable. Their faces share the same sharp angles and a soft, slight smile. Earl Smith and his wife, Ida, drive up from Lakewood and take NJ transit from Newark Penn Station to New York Penn Station for each home game.

They show the same vigilance as when J.R. was a 19-year-old rookie. The couple bought a home then in New Orleans. On road trips, said Earl Smith, he made sure he was waiting for J.R. in hotel rooms. In 2007, J.R. was the driver in an accident in Millstone Township that cost the life of a good friend. In 2009, he pleaded guilty to reckless driving and spent 24 days in jail. Earl Smith said he supported his son throughout the trauma.

While his son was with the Nuggets, where he spent five seasons, Earl Smith said he continued the mentoring that had J.R. making normal-range foul shots when he was only 3. But, he said, he also complained openly about Karl’s handling of his son. He said he told his son the "best shot is an open shot." As that translated onto the court, it often looked as though J.R. Smith had his own game plan.

Five weeks ago, Earl Smith practically predicted how the Knicks’ season would play out. Since then, his son has altered his style, and the Knicks have likewise adapted.

"You watch what happens when they turn to him," he said with knowing eyes. "Everything will be different."